Concentration-Dependent Effects of Insulin on Ca2+ Influx in Vascular Smooth Muscle Cells of Normotensive and Spontaneously Hypertensive Rats

1. The effect of insulin on cytosolic free Ca2+ concentration was measured using fura-2 in vascular smooth muscle cells of normotensive and spontaneously hypertensive rats. 2. In both strains, insulin increased cytosolic free Ca2+ concentration in a concentration range between 10−6 and 10−3 units/ml. The maximum increase in cytosolic free Ca2+ concentration was observed with 10−5 units/ml insulin (107 +25 and 82+27 nmol/l in spontaneously hypertensive rats and normotensive rats, respectively). 3. The effect of insulin was dependent on extracellular Ca2+ and was enhanced by stimulation of protein kinase C. 4. Thus insulin appears to induce a Ca2+ influx in vascular smooth muscle cells only over a certain range of concentrations. No significant difference in the response to insulin of cells from normotensive and hypertensive rats was observed.